Furnace

ABSTRACT

The invention relates to a furnace with a body ( 1 ) of a furnace, at the lower end of which a discharge device ( 2 ) for the ashes produced in the combustion chamber is provided. A continuous conveyor device in the form of a vibrating conveyor ( 3 ) is mounted below the discharge device ( 2 ). The vibrating chute of said vibrating conveyor reliably and effectively removes the dry ashes which are at the same time cooled with air.

BACKGROUND OF THE INVENTION

The invention relates to a furnace having

a firebox,

at least one discharge device disposed at the lower end of the fireboxfor combustion chamber ash, and

a conveyor disposed below the discharge device for the receipt andremoval of the discharged ash in a dry state.

The combustion chamber ash, which is withdrawn at the bottom from thefirebox, is obtained at a temperature of 800 to 1200° C. One originallyallowed the combustion chamber ash to fall into a water bath, from whichit was withdrawn via the conveyor. With modern low NO_(x) furnaces, theash quality has changed such that the subsequent transfer process wouldbe problematic due to the absence of an ability to remove water from theash. In addition, there were storage and removal problems.

On the basis of this background, a dry ash removal process was developedwith which the problem of removing water from the combustion chamber ashwas eliminated. In addition, the dry ash can be better reused or, afterappropriate processing, can even be mixed with the filter ash. In thisway there results a uniform removal mode for the entire ash of thebituminous coal furnace.

The known dry ash removal process is operated with a bituminous coalfurnace that is described in a prospectus of the U.S. American companyUnited Conveyor Corporation from the year 1997. The ash is collected onscreens or grids, and is introduced by batches into a vacuum transfersystem.

The object of the invention is to improve the cooling of the combustionchamber ash as well as the handling, removal and utilization thereof.

SUMMARY OF THE INVENTION

To realize this object, the initially mentioned furnace is inventivelycharacterized in that

the conveyor is embodied as a continuous-flow conveyor, and

a device for cooling the ash by means of air is provided.

It is proposed pursuant to an important further development of theinvention that the continuous-flow conveyor be embodied as a vibratingconveyor and have a vibrating trough that is open toward the dischargedevice.

Vibrating conveyors are extremely sturdy, which is of great significancewith regard to the abrasive characteristics of combustion chamber ash.In addition, such conveyors have high conveying capacities and readilypermit not only a discontinuous as well as a continuous operation, inother words, a very variable and effective dry ash removal process.

Above everything else, vibrating conveyors can be combined with a veryeffective air cooling. Thus, the temperature of the combustion chamberash can effectively, i.e. rapidly, be reduced to low values during theremoval.

In this connection, it is to be emphasized that the inventive means forthe removal and cooling of the combustion chamber ash arestraightforward, economical and reliable in operation.

The invention is primarily usable with bituminous coal furnaces,although it is also usable on other furnaces, such as lignite or browncoal furnaces, refuse incinerators, etc.

Pursuant to a further development of the invention, it is proposed thatthe base of the vibrating trough be provided with nozzle openings forthe cooling air. The cooling air passes through the ash deposited in thevibrating trough and can then pass into the firebox, in which it isutilized as preheated air for combustion. Alternatively, or in additionthereto, there is the advantageous possibility of providing thevibrating trough with lateral nozzle openings for the cooling air. Thisleads to a very intensive cooling of the upper surface of the ashdeposit in the vibrating trough and of the ash-particles that have justdropped down. Also in this case there results preheated combustion airfor the firebox. Finally, there is the possibility of also providing thedischarge device with nozzle openings for the cooling air. Thus, thecombustion chamber ash is already cooled in the counter flow prior tobeing deposited upon the vibrating conveyor, which leads to a veryintensive cooling and preheating of the air for combustion.

The introduction of cooling air as preheated combustion air into thelower region of the firebox has an additional advantageous effect,namely an afterburning of the combustion chamber ash. This improves thecombustion of the fuel (bituminous coal) furnace and reduces the amountof combustion chamber ash that is produced.

Depending upon the operating conditions, the underpressure that existsin the firebox can be sufficient to draw in the cooling air through theindividual nozzles. However, under certain circumstances it is alsoadvantageous to connect at least some of the nozzle openings to ablower. This can increase the throughput of cooling air and primarilyleads to an improved controllability of the cooling process. The dangerthat the nozzle openings become clogged is also reduced.

In addition to the above discussed direct cooling of the combustionchamber ash, pursuant to a further development of the invention anindirect cooling is also proposed, whereby the vibrating trough iscombined with an air receiver that is connected to the firebox. Thecooling air thus passes against the underside of the trough andwithdraws heat from the combustion chamber ash without coming in tocontact with the latter. Since the air receiver is connected to thefirebox, there again results preheated air for combustion.

It is readily possible within the scope of the invention to combine theindirect cooling of the combustion chamber ash with the direct cooling.

With the indirect cooling, it is advantageous to provide the undersideof the vibrating trough with cooling ribs or the like in order toincrease the heat transfer in a controlled manner.

Also with the indirect cooling the underpressure in the firebox cansuffice to draw the cooling air through the air receiver. Alternatively,there exists the possibly more advantageous possibility of connectingthe air receiver to a blower. The advantages relative thereto werealready described in conjunction with the direct cooling.

To the extent that a blower is used, whether with the indirect or withthe direct cooling, such a blower is preferably the fresh air blowerthat supplies combustion air to the firebox. A portion of thiscombustion air is thus branched off as cooling air and is introducedinto the combustion chamber as preheated air, and in particular eitherdirectly or also after being returned to the combustion air stream.

Pursuant to a further development of the invention, it is proposed thatthe discharge device be provided with an angled-off outlet and that thevibrating conveyor is disposed below the angled-off outlet. Thisconfiguration effects a considerable contribution to the cooling processsince the vibrating conveyor is not located in the direct radiationrange of the firebox. This improves the cooling, i.e. reduces therequired cooling capacity. In addition, it enables the use of fewerspecial or high-grade materials.

Pursuant to a further advantageous feature, the discharge device isprovided with closure dampers that offer the possibility of deliveringthe combustion chamber ash to the vibrating conveyor in a batch-wisemanner. Frequently, however, one will prefer a continuous ash discharge.In this case, the closure dampers then offer the possibility oftemporarily storing the ash if brief disruptions occur in the region ofthe vibrating conveyor or if minor repairs or maintenance work must becarried out. This eliminates the need for having to shut down thefurnace.

The main area of application of the invention is for bituminous coalfurnaces in power plants for the generation of steam.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail in the following withthe aid of preferred embodiments in conjunction with the accompanyingdrawing. The drawing shows in:

FIG. 1 in a schematic illustration, a cross-sectional view through asteam generator having a bituminous coal furnace;

FIG. 2 a side view of the furnace of FIG. 1;

FIG. 3 is a cross-sectional view through a modified embodiment of avibrating conveyor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The furnace of FIG. 1 has a firebox 1, at the lower end of which isdisposed a discharge device 2 for ash from the combustion chamber.Located below the discharge device 2 is a vibrating conveyor 3, thedirection of conveying of which extends perpendicular to the plane ofthe drawing.

The discharge device 2 has an angled-off outlet 4, so that the vibratingconveyor 3 has an offset arrangement and is not disposed in the directrange of radiation of the firebox 1. Thus, the vibrating conveyor 3 isthermally shielded. A non-offset arrangement is also possible.

The vibrating conveyor 3 has a vibrating chute or trough 5 that isdisposed in an air receiver or box 6. As indicated in FIG. 2, the airreceiver 6 is supplied with compressed air, and in particular via a line7 that branches off from a combustion air line 8. The air flows alongbelow the vibrating trough 5 and effects an indirect cooling of the ashthat is transported in the vibrating trough. To improve the transfer ofheat, the underside of the vibrating trough 5 is provided with coolingribs 9.

The air that is conveyed through the air receiver 6 is introduced aspreheated air for combustion into the furnace 1, and in particular inthe present case via a separate line 10. Alternatively, the preheatedair for combustion can also be returned to the combustion air line 8 andfrom there can pass either directly or via the burners into the firebox.

In contrast to the indirect cooling of the ash pursuant to FIGS. 1 and2, the vibrating conveyor 3 of FIG. 3 operates with direct cooling. Forthis purpose, provided in the base of the vibrating trough 5 are nozzleopenings 12 that blow the cooling air through the removed ash. Furthernozzle openings 13 are provided in the side walls of the vibratingtrough 5 in order to blow cooling air onto the upper side of the ash andat the same time to cool ash particles that drop down.

FIG. 1 further shows that the discharge device 2 is also provided withnozzle openings 14. These cool the ash particles that drop down incounter current, in other words, in a very effective manner, andfurthermore effect an afterburning of the ash, which minimizes thequantity of ash. Further cooling air openings can be associated with thefurnace or with the steam generator.

FIG. 1 finally shows that the discharge device 2 is provided withclosure dampers 15, of which the left one is closed for illustrationpurposes and the right one is illustrated as being half closed. Theclosure dampers 15 permit a discontinuous operation and duringcontinuous operation enable the brief elimination of tisturbances in theregion of the vibrating conveyor without it being necessary to shut downthe boiler plant.

Modifications are readily possible within the scope of the invention.For example, the indirect cooling can be combined with the directcooling. Furthermore, it is possible to operate with separate coolingair blowers. Under certain circumstances, it is possible to dispensewith any blower support to the extent that the underpressure in thefurnace is sufficient for drawing in the cooling air. However, a blowersupport has the advantage that appropriately high flow velocity in thenozzle openings can contribute to preventing the nozzle openings frombecoming clogged. This is also applicable for the nozzle openings thatare disposed in the region of the discharge device. If a blower supportis dispensed with, then the air receiver of the embodiment of FIG. 3 canbe eliminated. It is furthermore possible for a further vibratingconveyor to adjoin the vibrating conveyor of FIG. 2, with this furthervibrating conveyor also being provided with a cooling device, wherebythe two cooling devices can readily have different configurations.

The specification incorporates by reference the disclosure of Germanpriority document 199 35 597.5 filed Aug. 3, 1999 and Internationalpriority document PCT/EP00/07262 of Jul. 28, 2000.

The present invention is, of course, in no way restricted to thespecific disclosure of the specification and drawings, but alsoencompasses any modifications within the scope of the appended claims.

What is claimed is:
 1. A furnace comprising: a firebox; at least onedischarge device disposed at a lower end of said firebox for dry ashfrom a combustion chamber of said firebox; a continuous-flow conveyor,in the form of a vibrating conveyor, disposed below said dischargedevice for receiving and removing discharged ash in a dry state, whereinsaid conveyor is provided with a vibrating trough that is open towardsaid at least one discharge device, and wherein said vibrating troughforms an upper wall of an air receiver that adjoins said firebox; meansfor cooling said ash with air, wherein cooling air is utilized aspreheated combustion air for said firebox, and wherein a base of saidvibrating trough is provided with nozzle openings for the passage ofcooling air; and a blower, wherein said air receiver is connected tosaid blower.
 2. A furnace according to claim 1, wherein an underside ofsaid vibrating trough is provided with cooling means.
 3. A furnaceaccording to claim 2, herein said cooling means are cooling ribs.
 4. Afurnace according to claim 1 wherein said blower is also a combustionair blower.
 5. A furnace according to claim 1, wherein said at least onedischarge device is provided with an angled-off outlet, and wherein saidconveyor is disposed below said outlet.
 6. A furnace according to claim1, wherein said at least one discharge device is provided with closuredampers.
 7. A furnace comprising: a firebox; at least one dischargedevice disposed at a lower end of said firebox for dry ash from acombustion chamber of said firebox; a continuous-flow conveyor, in theform of a vibrating conveyor, disposed below said discharge device forreceiving and removing discharged ash in a dry state, wherein saidconveyor is provided with a vibrating trough that is open toward said atleast one discharge device, wherein said vibrating trough is providedwith lateral nozzle openings for cooling air, and wherein said vibratingtrough forms an upper wall of an air receiver that adjoins said firebox;and means for cooling said ash with air, wherein cooling air is utilizedas preheated combustion air for said firebox, and wherein a base of saidvibrating trough is provided with nozzle openings for the passage ofcooling air.
 8. A furnace according to claim 7, wherein said dischargedevice is provided with nozzle openings for cooling air.
 9. A furnaceaccording to claim 8, wherein a blower is provided, and wherein at leastsome of said nozzle openings are connected to said blower.
 10. A furnacecomprising: a firebox; at least one discharge device disposed at a lowerend of said firebox for dry ash from a combustion chamber of saidfirebox; a continuous-flow conveyor, in the form of a vibratingconveyor, disposed below said discharge device for receiving andremoving discharged ash in a dry state, wherein said conveyor isprovided with a vibrating trough that is open toward said at least onedischarge device, and wherein said vibrating trough forms an upper wallof an air receiver that adjoins said firebox; and means for cooling saidash with air, wherein cooling air is utilized as preheated combustionair for said firebox, wherein a base of said vibrating trough isprovided with nozzle openings for the passage of cooling air, andwherein said cooling air is introduced as preheated combustion air intoa stream of combustion air.